1. Field of the Invention
The present invention relates to a method of making an aluminum reflecting mirror in which a protective film, an aluminum reflective film, and a transparent protective film comprising a plurality of layers are laminated on a glass substrate; and to the aluminum reflecting mirror made in accordance with the method to which the invention relates.
2. Description of the Prior Art
Various kinds of aluminum reflecting mirrors for use in optical apparatus have conventionally been developed.
For example, Japanese Unexamined Patent Publication No. 5-150105 discloses an aluminum reflecting mirror in which a surface of a substrate made of glass, plastics, or ceramics is smoothed, a protective film made of SiO2 is formed on the surface of substrate, a reflective film made of Al is formed on the protective film, and a transparent protective film is formed on the reflective film, whereas the transparent protective film comprises an MgF2 film, a TiO2 or CeO2 film, and an Al2O3 film.
When Al is directly deposited on a glass substrate, the Al reflective film may be corroded by ingredients precipitated from the glass substrate. Therefore, the SiO2 film is formed between the glass substrate and aluminum reflective film in the aluminum reflecting mirror disclosed in the above-mentioned publication, so as to prevent the aluminum reflective film from corroding, for example.
Also, the transparent protective film in which an MgF2 film, a TiO2 or CeO2 film, and an Al2O3 film are laminated on the aluminum reflective film is formed in order to protect the aluminum reflecting film and improve its environmental resistance.
While Al2O3 is deposited as the outermost transparent protective film in the above-mentioned conventional aluminum reflecting mirror, Al2O3 cannot be deposited by resistance-heating deposition method but by electron bombardment method using an expensive electron gun, which increases the cost of equipment.
Also, while the deposition of each layer and the like must be carried out in a vacuum atmosphere when making an aluminum reflecting mirror, it takes a certain extent of time for attaining the vacuum atmosphere within a chamber. Therefore, for improving the manufacturing efficiency, it is necessary that all the materials for forming the substrate, protective film, aluminum reflective film, and transparent protective film be accommodated within the chamber and then the chamber be evacuated, so as to continuously carry out the deposition of individual layers and the like.
Since different materials are used for the protective film, aluminum reflective film, and individual layers of the transparent protective film, however, a space for accommodating all these materials is necessary in the above-mentioned conventional aluminum reflecting mirror. Further, instruments used for resistance-heating deposition method and an electron gun must be provided, which increases the size of chamber.
In view of the circumstances mentioned above, it is an object of the present invention to provide a method of making an aluminum reflecting mirror by which all the layers can be formed by resistance-heating deposition method whereas the size of manufacturing equipment can be reduced, and an aluminum reflecting mirror.
In order to achieve the above-mentioned object, the present invention provides a method of making an aluminum reflecting mirror in which first to fifth layers are laminated on a glass substrate successively from the glass substrate side, the method comprising:
a step of evacuating a chamber accommodating therein the glass substrate and respective materials for forming the first to fifth layers;
a step of forming the first layer as a protective film by depositing SiO on the glass substrate;
a step of forming the second layer as an aluminum reflective layer by depositing Al on the first layer;
a step of forming the third layer as a transparent protective layer by depositing MgF2 on the second layer;
a step of forming the fourth layer as a transparent protective layer by depositing CeO2 on the third layer; and
a step of forming the fifth layer as a transparent protective layer by depositing SiO2 on the fourth layer while introducing O2 gas into the chamber.
The step of forming the third layer may comprise:
a first step of depositing MgF2 at a deposition temperature lower than 80xc2x0 C.; and
a second step of depositing MgF2 at a deposition temperature higher than 300xc2x0 C.
Each of the first to fifth layers may be formed by resistance-heating method.
The step of forming of the third layer may be carried out such that a lower layer thereof is formed by lower-temperature deposition, and then an upper layer thereof is formed by higher-temperature deposition.
The present invention provides an aluminum reflecting mirror in which first to fifth layers are laminated on a glass substrate successively from the glass substrate side;
wherein the first layer is a protective film formed by depositing SiO, the second layer is an aluminum reflective film formed by depositing Al, the third layer is a transparent protective film formed by depositing MgF2, the fourth layer is a transparent protective film formed by depositing CeO2, and the fifth layer is a transparent protective film formed by depositing SiO2.
The third layer may comprise a two-layer structure composed by a lower layer formed by lower-temperature layer and an upper layer formed by a higher-temperature deposition.